I am thinking of using a long piece of LVL beam (1.75" thick by 12") wide as a base to mount two lathe beds end to end for increasing the distance between centers. Does anyone know how stable the LVL beam is and if it warps or not?
Not nearly stable enough to keep two lathe beds indexed to each other. It's still a piece of wood, albeit one with a hell of alot of glue in it. I suppose if you were to seal it very thourougly you might increase your odds quite a bit.
I use truckloads of LVL material in the custom homes I frame. While they are a godsend in my industry as a replacement for sawn lumber, they are still a wood product.
Rarely do I see any evidence of twist or bow in them, but they regularly can be found to cup if left to the weather on top of a lumber pile.
if you bolted several together and notched them for metal plates to use for "feet", you could probably do some coarse work. but why go to that amount of work, it would be easier to pour concrete. or do what some here do, make lathe tables out of cinder block. --Loren